The present invention relates generally to scatter-correction for X-ray or the like type of examination technique, and more specifically to a scatter-correction technique for situations wherein the angle of incidence of an incident ray from a radiation source impinges on a detector at an angle which is not exactly zero degrees or exactly at right angles to the detector, and thus allows for the source to be moved with respect to the detector or vice versa.
Breast cancer is a significant cause of mortality among women in the United States. Currently the most widespread breast-cancer screening technique is X-ray mammography, where malignancies are detected based on their characteristic shape (typically spiculated) and radiological density (similar to breast glandular tissue).
Early detection of breast cancer generally improves a patient""s chance of survival and is thus of critical importance. The task of detection of malignancies is complicated by the fact that the breast is a radiologically complex 3D structure that is imaged by 2D X-ray projection. Thus, malignant lesions can be masked by surrounding glandular tissue, decreasing contrast and distorting the lesion""s perceived shape. A significant number of malignancies are missed in mammography because of the presence of this increase of structural noise brought about by the projection of 3D structures in the breast onto a 2D image.
Tomosynthesis is a promising alternative to conventional two-dimensional mammography. This imaging technique resides in the acquisition of plural low-dose 2D X-ray projection images, where the X-ray source is moved along an arcuate trajectory with respect to the stationary breast and/or detector. X-ray projections are thus acquired at different angles. These angular projections are then combined in a 3D image reconstruction of the breast. In the reconstructed image, the overlap of 3D structures is mitigated, contrast is enhanced and the morphological features of malignancies (speculation) can be better preserved than in 2D X-ray imaging, therefore leading to improved sensitivity and specificity with respect to 2D X-ray mammography.
In tomosynthesis, the use of a non-stationary X-ray source precludes the use of a traditional grid for scatter rejection. With larger source angles with respect to the detector normal, the scatter signal will increase due to the longer distances that the X-rays traverse through the breast tissue. Therefore, there is a need to be able to estimate the scatter component on an X-ray image that has been acquired and compensate for the scattering in order to improve the resolution/effectiveness of the examination of the breast tissue.
More specifically, a first aspect of the present invention resides in a method of estimating scatter in an image, where radiation from a radiation source is transmitted through an object to be imaged and is incident on a detector at an inclined or xe2x80x9cnon-zeroxe2x80x9d angle. This method comprises explicitly modeling an effect of angular incidence of the radiation on a scatter signal, including deriving, using an empirically based correction which includes the effect of a non-zero angle of incidence of the radiation on the detector, an estimate of the scatter signal in image data derived from the incident radiation on the detector.
A second aspect of the invention resides in a method of calculating and removing scatter from an image, where radiation emitted from a source is transmitted through an imaged object, is incident on a detector at a non-zero (acute) angle, comprising: explicitly modeling the effect of angular incidence of radiation in a scatter signal; re-normalizing the scatter signal depending on the angle of incidence of radiation and the thickness of the object imaged; and correction of scatter from an image based on inverse-filtering.
A third aspect of the invention resides in a method of estimating scatter in an X-ray image, where radiation emitted from an X-ray source is transmitted through an imaged object and is incident on the X-ray detector at an acute or non-zero angle, comprising: explicitly modeling the effect of angular incidence of X-ray radiation in a scatter signal; and calculating, via convolution, an estimate of the scatter signal in an X-ray image.
A fourth aspect of the invention resides in a method of estimating an asymmetrical scatter kernel wherein asymmetry is introduced by angular incidence of radiation, which has been emitted from a source and transmitted through an object to be imaged, on a detector, comprising: modifying scatter that would be derived wherein the radiation is directly incident on the detector with zero degrees of inclination, using an asymmetry factor which indicates the shape and magnitude of the scatter kernel and which varies with an angle at which the radiation is incident on the detector, a mean attenuation coefficient of the object, and a distance the radiation has traveled through the object.
Further aspects of the invention respectively reside in computer readable media which are encoded with programs executable by a computer for implementing the above mentioned methods. Additionally imaging systems which include hardware and computer software and which are adapted to implement the above mentioned methods, also comprise further aspect of the invention.